Helen Jenkins
Nutrition

How to get your carbohydrate intake right

What nutrition to take when you're training for a triathlon, how much and when

Completing a triathlon is a huge physical and mental challenge, with many races being amongst the toughest endurance events in the world. Nutrition plays a key role in race success and can be the difference between a personal best and failing to reach the finish line. But how do you get carb intake right? Jill Leckey, senior nutritionist at Science in Sport, reveals all…

Carbohydrate is the main energy source during high intensity exercise and depending on race pace, stores can be depleted following 90 minutes. This stresses the importance of carbohydrate intake prior to an event to ensure muscle storage capacity is optimised and additionally, the requirement for fuelling during exercise. Carbohydrate ingestion during exercise is known to improve performance and race times and delay the onset of fatigue. 

Race day nutrition 

Breakfast on race day is simply to top up carbohydrate stores, therefore it is important not to overeat as this can result in feeling bloated. Choosing a simple option such as porridge, wholemeal toast and apple juice 2-3 hours before is likely to be sufficient, although choices will vary depending on individual preference. 

The most common question in relation to carbohydrate intake is how much to consume during exercise. Carbohydrate should be consumed during endurance events at a rate of 60 g per hour to optimise carbohydrate oxidation rates. This recommended value does not change between males and females. Practical options include homemade flapjacks, cereal bars, energy gels, energy bars and carbohydrate fluids, all of which contribute towards the 60g per hour. 

Energy gels and carbohydrate and electrolyte fluids are common choices because of their rapid digestion rates in comparison to more solid foods; the former also supports both hydration and fuelling. Personal preference plays a huge role in race day nutrition and strategies should be tested in training to assess what works best for you, this helps to prevent gastrointestinal distress on race day. 

Is a glucose: fructose sports drink better than a glucose only drink?

It is well known that consuming a glucose drink during endurance exercise is beneficial to sporting performance, but does the addition of fructose provide a further benefit to consuming a solely glucose drink?

Both glucose and fructose are simple sugars however one of the significant differences is their glycemic index, which describes how quickly they increase blood glucose. Glucose is rapidly digested and has a high glycemic index whereas fructose is slower to digest and has a significantly lower glycemic index. Glucose and fructose are also metabolised differently, whilst glucose can be metabolised directly at the muscle, fructose is metabolised via a different pathway requiring an enzyme present in the liver. 

In addition, glucose and fructose use different transporters for movement into the muscle cells. Maltodextrin, which is a glucose polymer used in many available sports drinks has a bland taste, therefore product developers often add a small amount of fructose which increases the level of sweetness and enhances the taste.

What does this mean for endurance exercise?

For a glucose and fructose combination to be advantageous to endurance performance, glucose transporters must be saturated. This occurs when greater than 60 g of glucose is consumed per hour for example through fluid, gels or bars. If glucose and fructose combinations are consumed in suboptimal amounts (with less than 60 g of glucose) which is typically the case, then there is no further benefit to sporting performance and in fact this can hinder performance through negative effects on blood glucose and carbohydrate metabolism.

This means that for the addition of fructose to be effective in relation to sporting performance other than for the purpose of taste, it should consumed with greater than 60 g of glucose per hour and the endurance event should last for longer than 2 hours in duration.

Jill Leckey is Senior Sports Nutritionist for Science in Sport (SiS) www.scienceinsport.com


 
 

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